Since the laser's inception, it has gained increasing acceptance in the industrial market as being a manufacturing tool that can increase efficiency and improve quality. The laser's increasing acceptance is due, in large part, to: its noncontact operational characteristic which eliminates costly fixturing; its easy automation and integration into manufacturing processes; its potential for greatly reducing process times; and its ability to access remote locations and be shared by several workstations for multiple processing. High power lasers are now being used in industry for a number of manufacturing applications including boring, cutting, welding, heat treating, and general machining.
Weld quality is a primary concern in industrial laser welding processes. Since many process variables can influence the quality of a laser weld (such as power, frequency, weld speed, focal length, position, workpiece composition, joint fit up, and shield gas), it is necessary to be able to determine the penetration of the weld independent of such process variables. Penetration of a weld is, probably, the single most important indicia of weld quality with a measure of same being required to permit adjustment of the process variables. By using appropriate process controls in which one or more of the aforementioned process variables are adjusted, the quality of the weld may be maintained within predetermined limits. The welding process can be monitored and controlled effectively if at least one measurable output can be related to the physical process of welding. Many process monitoring devices have been used for laser weld processed materials without notable success.
A method and apparatus for monitoring laser beam welding, illustrated in U.S. Pat. No. 5,155,329 issued Oct. 13, 1992, generally involves monitoring the intensity of light of predetermined wavelength emanating from a workpiece immediately before there is a rise in the intensity of an associated pulsating laser beam and correlating the emanating minimum light intensity with the depth of penetration of the laser weld zone. Since the weld depth of penetration is correlatable with the minimum intensity of emanating light prior to a rise in the intensity of the pulsating laser beam, the pulsating laser beam's intensity must be monitored as well as the emanating light intensity of the predetermined wave length. Accordingly, such method and apparatus involve a degree of complexity which is undesirable.
The present invention is directed to overcoming one or more of the problems set forth above.